Calculations
How to Calculate Aggregate Quantity Alongside Bitumen
Bitumen calculators output bitumen quantity, but the aggregate order — usually the bigger line item on your budget — comes from the same numbers.
Most people calculating bitumen requirements are also, whether they realize it or not, one step away from having their full aggregate order too — because aggregate is simply the remainder of the mix weight once bitumen is subtracted.
Aggregate weight
Aggregate Weight = Total Mix Weight − Bitumen Weight
This works because asphalt mix, by definition, is only aggregate plus bitumen binder (filler is typically counted within the aggregate/mineral fraction).
Worked example
You’ve calculated a total mix requirement of 47 tonnes at 5.5% bitumen content for a wearing course.
- Bitumen weight = 47,000 kg × 5.5% = 2,585 kg
- Aggregate weight = 47,000 kg − 2,585 kg = 44,415 kg (44.4 tonnes)
That 44.4 tonnes is what you order from the quarry or aggregate supplier — it already accounts for the fact that some of your total mix weight is bitumen, not stone.
Why this step gets skipped (and shouldn’t)
On smaller jobs, contractors sometimes order aggregate by area and thickness alone, without separating out the bitumen fraction — this leads to consistently over-ordering aggregate by roughly the bitumen percentage (5–7% of the total, which adds up fast on large-volume projects). If you’re calculating from an asphalt plant’s perspective rather than a finished-mix perspective, the plant needs the aggregate figure specifically, not the combined mix figure, to place its own raw material order.
Aggregate is usually bought and priced separately from bitumen
Even though both go into the same finished asphalt mix, aggregate (crushed stone, sand, filler) and bitumen binder are typically sourced from entirely different suppliers with different pricing structures. Separating the two figures early avoids budgeting confusion later.
Aggregate gradation still matters beyond total weight
The total aggregate weight figure tells you how much to order overall, but it doesn’t tell you the breakdown by size fraction (coarse, fine, filler) required by your job mix formula — that breakdown comes from the mix design’s gradation curve, not from this calculation. Treat the aggregate weight from this method as the total tonnage to source, then apply your mix design’s percentage breakdown by sieve size to place individual material orders.
The calculator outputs aggregate weight automatically alongside bitumen — try it